You can use randomly placed
letters to create interesting dynamic art from your photos. For example
a simple forest photograph...

...can be given a vignette
frame of exclamation marks and question marks:

A happy face
can be given a surround of letters from the word "HELLO!":

Or build a logo
from a colorful alphabet...

This filter places
characters symbols and letters in a chaotic way across your image, though
of course you can choose to make it less random using the dialog box.
A more "regular" text effect is the the Text
Effect.